In many air conditioners, power converters which convert commercial alternating-current power to certain alternating-current power are used to supply power to a motor of a compressor. These power converters include, for example, a direct power converter for alternating current which directly converts alternating-current voltage to a desired alternating-current output, and is typically represented by a so-called matrix converter. This matrix converter does not need a large capacitor which smoothes a voltage ripple caused due to commercial frequencies, nor a reactor, and therefore it is expected that the size of the power converter can be reduced. The matrix converters have been gaining attention as next-generation power converters (see, for example, Patent Document 1).
Various attempts to improve efficiencies of such power converters have also been made. For example, there is a case in which a reverse blocking diode is connected in series to a switching element used in a power converter to ensure resistance to a reverse bias. However, the provision of such a reverse blocking diode increases conduction loss, and inhibits improvement in efficiency. To solve this problem, a reverse blocking insulated gate bipolar transistor (IGBT) which does not need a reverse blocking diode and is capable of reducing a reduction in an ON voltage of a switching element is suggested as a switching element (see, for example, Non-Patent Document 1).